Method of treating hydrocarbon oil



P. c, KEITH; JRI METHOD OF TREATING HYDROCARBON on.

June 1, 1937.

Filed June 13, 1933 INVENTOR PERCIVAL C. KEITH JR.

ATTORNEY Patented June 1, 1937 UNITED STTES ATENT OFFICE Percival C. Keith, Jr., Port Washington,

assignor to Gasoline Products Company, Newark, N. J., a corp N. Y., Inc., oration of Delaware Application June 13, 1933, Serial No. 675,542

3 Claims.

The present invention relates to the conversion of relatively high boiling hydrocarbon oils into relatively low-boiling hydrocarbon oils, for example oils suitable as fuel for internal combustion engines. I

In certain conversion processes the oil is raised to and maintained at cracking temperature under a relatively high superatmospheric pressure for a predetermined period of time. The oil is then passed into a zone of substantially lower pressure wherein a substantial portion of the conversion products, with the exception of the heavy tar-like residues, is vaporized by the contained heat of the oil. The tarry residues are withdrawn from the system and the vapors are subjected to fractional condensation whereby the constituents heavier than those desired in the distillate product are condensed and separated from the desired low boiling products, such high- 1 er-boiling portions, if desired, being returned with added fresh stock, to the original cracking operation.

It is an object of my invention to provide an improved method of preheating and vaporizing the fresh charging stock prior to the introduction thereof into the cracking zone of a process of the type mentioned hereinbeiore.

In accordance with my invention hydrocarbon oil is subjected to heating under superatmospheric pressure to raise the oil to a conversion temperature and is then subjected to digestion while still under superatmospheric pressure, for a period of time suiiicient to cause additional conversion. Subsequently the digested products are introduced into an evaporating zone, held under lower pressure, wherein separation of vapors from liquids takes place. Fresh charging stock, which may be dirty, that is, of marked coke forming characteristics, and relatively heavy, is introduced into this zone for vaporization and also slight cracking of a viscosity breaking nature, the necessary heat being supplied by conducting a portion of the hot oil at furnace coil outlet temperature from the heating operation directly to the evaporating zone without additional digestion and accompanying loss of temperature. Vapors are withdrawn from the evaporating zone a desired product, and a side stream of clean distillate stock is also withdrawn from said evaporating zone. This clean distillate stock is then subjected to the heating operation first mentioned.

The above mentioned and further objects and advantages of my invention and the manner of for fractionation to produce attaining them will be made clear in the following description taken in conjunction with the accompanying drawing.

The drawing illustrates diagrammatically an oil cracking system embodying my invention.

Referring more specifically to the drawing, ref-- erence numeral i indicates a furnace, 2 a digester or reaction chamber, 3 an evaporator tower, 4 a fractionator tower, 5 a final distillate receiving drum, and 6 a fuel oil flash tower. Fresh charging stock, such as for example 29-33 A. P. 1. Wyoming green reduced crude or gas oil is introduced through pipe line I by action of pump 8 and passes consecutively through coil 9, heat exchanger IO and coil l i into the evaporator tower 3, above baffle plates l3, where it mixes with hot products introduced into the tower through line l2 below the baffle plates. The heat of these hot products serves to raise the fresh charging stock to a moderate cracking temperature suflicient to cause a small degree of conversion of said stock of'a viscosity breaking nature and to vaporize the lighter fractions thereof, leaving a heavy tar-like residue.

The vapors of the lighter fractions pass upwardly through the evaporator tower and are partially condensed by the cooling action of coil M. The heavier condensed fractions are collected on trap-out tray l5 and delivered through pipe l6 into the base of fractionating tower 4', which serves as an accumulator drum. The uncondensed lighter fractions travel through vapor line I! into the fractionating tower entering above the point of connection of pipe l6 and are subjected to fractionation, the necessary cooling action being supplied by coil 9. Fractionated vapors of the desired end point are removed from the top of the tower through conduit f 8 and condenser I9, the resulting condensate being collected in receiver 5. By-pass valve 20 'is furnished for varying the amount of oil passing through coil 9 and thereby controlling the fractionating action of the tower.

Reflux condensate from the fractionation of the vapors in tower 4, mixed with the condensate from pipe i6, collects in the bottom of the tower which acts as a reservoir. This mixed liquid is a clean distillate and constitutes the charging stock for the cracking furnace or heater I, through which it is forced by action of pump 2|. This pump forces oil withdrawn from the bottom of tower 4 through pipe 22 to the heater, or alternatively through pipe 23 and coil H! to the heater, the desired flow being secured by manipulation of valves 24 and 25.

During its passage through the coils of heater l the oil is raised to a relatively high cracking temperature of, for example, 875 to 940 F. under a superatmospheric pressure preferably in excess of 400 pounds per square inch, a particularly suitable range being from 750 to 900 pounds per square inch, the highly heated products being thereafter introduced into the digester or reaction chamber 2 through line 26. The reaction chamber is maintained under temperature and pressure conditions approximating those of the coil outlet, e. g. 750 pounds per square inch and an average temperature of 925 F. the chamber outlet temperature generally being 40 or F. lower than its inlet temperature, and in this chamber the products are subjected to further cracking or conversion of heavier products to lighter products.

The digested products pass from the reaction chamber into the evaporator 3 through pipe line l2, the pressure thereon being reduced by action of valve 2'5, to a pressure considerably lower than that of the reaction chamber, but generally exceeding 109 pounds per square inch. For example, a pressure of from 125 to 225 pounds may be maintained in the evaporator, a preferred range being from 150 to 206 pounds. Under these conditions a substantial vaporization of lightproducts takes place but at the same time a moderate cracking temperature, preferably from 800-830 is maintained to insure light cracking of the fresh charge and production of a residue of low viscosity. This temperature is insured by by-passing hot oil products directly from the heater to the evaporator through by-pass line 28, the desired control being effected by valves 29, 38, and Si.

By this direct introduction the heat required for the evaporation of the components derived from the fresh charging stock is obtained from the digested products leaving the reaction chamber. Furthermore the fairly high temperature thus secured in the base of the evaporator tower is effective in securing viscosity breaking cracking of the fresh stock.

Generally in operation about 10% of the products leaving the heater are by-passed around the reaction chamber into the base of the evaporator tower, but this proportion is not invariable; sometimes the amount of heat needed will be considerably less and the by-pass line may be shut 01f altogether, depending on the quantity of oil in the base of the fractionator tower, which acts as a composite feed tank. But when the supply of composite feed oil falls off it is necessary to increase the fresh charging rate and at the same time by-pass the reaction chamber to obtain enough heat to vaporize this additional fresh stock. The gravity of the unvaporized tar-like residue would remain approximately the same in any case.

Tar is withdrawn from the base of the evaporator and introduced through pipe 82, having pressure reducing valve ii, into flash tower 6 wherein as a result of the reduced pressure lighter products separate as vapors, leaving a heavy resi due. The vapors pass off through vapor line 33, are condensed in condenser st and stored in receiver 35. Condensate may be withdrawn from this receiver and forced by pump 36 to line 31 into the top of evaporator 3 as a refluxing medium, or through line 38 into the base of fractionator 4 as part of the composite feed stock. Valves 39 and 4!} provide the necessary control. The heavy residue is eliminated from tower 6 through drawoif line 39 and heat exchanger H], for storage or further independent treatment.

While I have described a particular embodiment of my invention for the purposes of illustration it should be understood that various modifications and adaptations which will occur to one skilled in the art may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. The process of treating hydrocarbon oil which comprises heating a clean distillate cracking stock to cracking temperature under superatmospheric pressure, introducing the larger part of the resulting heated oil into a reaction zone held under superatmospheric pressure wherein conversion into lighter products takes place, conducting the digested oil from said zone into an evaporating zone held under reduced pressure wherein separation of vapors from liquids takes place, withdrawing vapors from said evaporating zone and introducing them into a fractionating zone wherein fractional condensation thereof occurs, removing fractionated vapors from said fractionating zone and condensing them as a desired product, removing liquids from said evaporating zone and introducing them into a flashing zone of lower pressure wherein separation of vapors from liquids takes place by the contained heat of the oil, removing resulting vapors from said flashing zone, condensing them and introducing resulting condensate into said evaporating zone as a refluxing medium, passing fresh relatively heavy charging stock in indirect heat exchange relation with vapors in said fractionating zone, then in indirect heat exchange relation with vapors in said flashing zone, introducing the resulting preheated charging stock into an intermediate portion of said evaporating zone so that said charging stock passes downwardly in countercurrent heat exchange with hot rising vapors, to cause dephlegmation of said vapors and stripping of said charging stock, simultaneously introducing a portion of the heated oil from said cracking zone directly into said evaporating zone in quantities sufficient to maintain the base of said evaporating zone at a cracking temperature so as to cause light cracking of said fresh charging stock, forming a heavy condensate said evaporating zone at a point above that of the introduction of said fresh charging stock, removing condensate so formed and introducing it into the base of said fractionating zone, and removing reflux condensate from said iractionating zone and utilizing said condensate as said clean cracking stock first mentioned.

2. A process in accordance with claim 1 wherein the reflux condensate withdrawn from the fractionating zone is passed in indirect heat exchange relation with the vapors in said evaporating zone prior to the utilization of the reflux condensate as the clean cracking stock first mentioned.

3. A process in accordance with claim 1 wherein the amount of heated oil introduced directly from the heating zone into the evaporating zone is about ten percent of the total amount of oil passing through the heating zone.

PERCIVAL C. KEITH, JR. 

